Naive CD4+ T-cells require two independent signals in order to be successfully activated and capable of undergoing clonal expansion (Janeway, Cold Spring Harbor Symp. Quant. Biol. 54:1-14 (1989)). The first signal is achieved by stimulation through the T-cell receptor by immunogenic peptides presented by MHC class II molecules on antigen presenting cells (APC) (Weiss, J. Clin. Invest. 86:1015 (1990)).
In addition, a second signal, referred to as costimulation, is also required. This costimulatory signal is generally provided through the ligation of CD28 on the T-cell and its inducible counter-receptor CD80, or CD86 on the APC (Linsley et al, J. Exp. Med. 173:721-730 (1991)).
The modified single chain Fv (sFv) molecules of the invention, when expressed on a cell surface, act as artificial co-stimulatory ligands. They were constructed to enhance an immune response to disease.
Others have constructed sFv molecules for purposes of intracellular targeting to combat disease (Biocca and A. Cattaneo, (1995) Trends in Cell Biology 5:248-252). However, the sFv molecules so constructed did not comprise a transmembrane domain which could be anchored to an extracellular surface (Biocca and Cattaneo, supra).
sFv molecules are one example of a myriad of molecules that are being tested for potential therapeutic and diagnostic uses against disease. Additional molecules of this type are needed.
The modified sFv molecules of the present invention stimulate adhesion between cells thereby enhancing an immune response against disease. These molecules generally comprise a binding site of an antibody and at least a portion of a transmembrane domain of a cell surface receptor.
In one embodiment of the invention, the modified sFv molecule further comprises a linker which connects the binding site to at least a portion of the transmembrane domain. In a specific embodiment, the modified sFv molecule comprises a binding site which recognizes and binds the CD28 receptor, a Fc portion of an antibody, and at least a portion of a transmembrane domain. In this embodiment, the binding site has two variable regions (VH and/or VL chains) and the Fc portion connects the binding site with the transmembrane domain.